1. Field of the Invention
The present invention relates generally to determination of the identity of surface agents such as surface-deposited chemicals.
2. Description of the Background Art
The identification of chemical agents may be conducted under adverse conditions. Such identification may be carried out, e.g. in the field, or at a material entry point. Chemical agents to be identified, may be e.g. hazardous or toxic. Personnel engaged in such identification may wish to be protected from the chemicals by an enclosure. In this way equipment used to perform the identification may be exposed to the substance, while the personnel who operate the equipment are not.
Raman spectroscopy is one means of identifying unknown chemical agents. Raman spectroscopy equipment, however, is typically designed for static placement in laboratories, and may therefore lack ruggedness and mobility. Raman spectroscopy equipment may not be adapted to relative motion between the equipment and an unknown chemical agent. Such equipment may be large and heavy, and the individual components may not be integrated to the degree required for use in the field.
Raman spectroscopy equipment may be placed next to, e.g. a conveyor system carrying objects of various shapes or sizes, on a vehicle, or next to a gate through which objects, such as, e.g. vehicles may be traveling. In cases such as these there may be relative motion between the Raman spectroscopy equipment and the chemical agent to be analyzed.
Ray et al., xe2x80x9cUltraviolet mini-Raman LIDAR for Stand-off, in situ Identification of Chemical Surface Contaminantsxe2x80x9d, e.g. describes a related device using the Raman effect. The device is described as portable and rugged enough to be transported in a standard minivan, and capable of operating within minutes of arriving at a scene.
Raman spectroscopy equipment used in a laboratory may have a relatively long time window in which to view a sample. A laboratory sample may be analyzed several times to determine of its identity. Raman spectroscopy equipment that is placed next to a conveyor or on a vehicle, on the other hand, may have only a limited period of time in which to analyze a chemical agent. It would thus be desirable for mobile Raman spectroscopy equipment to be able to analyze a chemical agent in a relatively brief period of time, as e.g. a vehicle traverses the ground or a package moves along a conveyor system. It would also be desirable for the identity of a chemical agent to be determinable in a limited number of pulses of, e.g. an output beam.
Raman spectroscopy equipment that is mounted on an operational vehicle or alongside a conveyor system may be, e.g. located within in short distance, such as, e.g. two meters, of a chemical agent. It would thus be desirable for Raman spectroscopy equipment to be capable of efficient light collection at that range. Moreover, a distance between the Raman spectroscopy equipment and a chemical agent may vary significantly over time due to, e.g. rugged terrain or a random placement of packages on a conveyor. It would thus be desirable for an optical system to be capable of adjusting its focus to compensate for distance variation.
In the event Raman spectroscopy equipment may be used, e.g. in military applications, the equipment may be required to operate for extended periods of time without extensive maintenance. It would be desirable, therefore, for the equipment to be able to function reliably for extended periods of time.
Raman spectroscopy equipment may become contaminated by the chemical agents which it analyzes. Raman spectroscopy equipment is normally decontaminated by, e.g. washing it with a chemical, such as, e.g. a chemical solvent. The decontamination process may, however, harm sensitive components comprising the Raman spectroscopy equipment. It would be desirable for Raman spectroscopy equipment to be resistant to contamination from the chemical agents to be analyzed. It would further be desirable for Raman spectroscopy equipment that will be decontaminated to be resistant to chemicals used during the decontamination process. It would further be desirable for Raman spectroscopy equipment that is mounted outside a vehicle or an enclosure to offer no contamination path into the vehicle or enclosure.
In the event that Raman spectroscopy equipment uses an Excimer laser, the gas inside the Excimer laser may have to be replaced periodically. It would be desirable, therefore, for such a replacement to be relatively quick and easy to perform, so the operation of the equipment is interrupted minimally.
Fluorescence of, for example, the surroundings of a chemical agent may interfere with determining an identity of the chemical agent. Soils, in particular, exhibit significant fluorescence when subjected to laser light. It would be desirable, therefore, for the effect of such fluorescence on the analysis of chemical agents to be minimized.
Raman spectroscopy equipment may well be unable to identify a particular chemical agent. The inability to identify the chemical agent may be due to, e.g. the chemical agent having not been encountered previously, or a malfunction of the equipment. It would be desirable for Raman spectroscopy equipment that comes upon a new or unidentifiable substance to be able to store a signature of the chemical agent for later analysis or troubleshooting. In the meantime, it would be desirable for a list of known chemical agents to be updated to include the new or unidentifiable chemical agent so that a frequency of occurrence of the chemical agent can be determined.
There remains a need in the art, therefore, for a transportable Raman spectroscopy device that is capable of analyzing chemical agents moving relative to the device, in the presence of soil fluorescence, without being compromised unduly by decontamination procedures.
The invention provides a relatively compact, lightweight, piece of Raman spectroscopy equipment.
In particular, in one aspect the invention provides an apparatus for laser interrogation of surface agents moving relative to the apparatus. A receiver telescope includes a secondary reflector that may compensate for variations in distance from a target to the laser. The secondary reflector relies on a distance to target signal that may be collected at a point substantially away from the target, in the direction of relative motion, to allow a focusing mechanism time to react.
In a second aspect the invention provides an apparatus for laser interrogation of surface agents moving relative to the apparatus. A receiver telescope includes a secondary reflector that may compensate for variations in distance from a target to the laser. The secondary reflector relies on a distance to target signal that may be collected at a point substantially away from the target, in the direction of relative motion, to allow a focusing mechanism time to react. The laser may emit pulses at a predetermined pulse rate, a variable pulse rate, an operator-controlled pulse rate, or a pulse rate that is proportional to a rate of relative motion of a target relative to the apparatus or a ground rate of relative motion of a vehicle.
In a third aspect the invention provides a system for laser interrogation of surface agents moving relative to the apparatus. A receiver telescope includes a secondary reflector that may compensate for variations in distance from a target to the laser. The secondary reflector relies on a distance to target signal output by a range finding means that may be collected at a point substantially away from the target, in the direction of relative motion, to allow a focusing mechanism time to react. The focusing means focuses the secondary reflector based on the distance-to-target signal and the rate of relative motion. A spectrograph receives the inelastically scattered radiation from the receiver telescope.
In a fourth aspect the invention provides a method for laser interrogation of surface agents moving relative to an interrogator in which a receiver telescope compensates for variations in distance from a target to the laser. The secondary reflector relies on a distance to target signal that may be collected at a point substantially away from the target, in the direction of relative motion, to allow a focusing mechanism time to react.
A spectrograph receives the inelastically scattered radiation from the receiver telescope, comparing the image of the dispersed spectrum of the target substance to an image of a spectrum of inelastically scattered radiation of a known substance, identifying the target substance if the image of the dispersed spectrum of the target substance matches substantially the image of the inelastically scattered radiation of the known substance, and adding the target substance to a list of unidentified substances if the image of the dispersed spectrum of the target substance does not substantially match any image in database.
In a fifth aspect the invention provides a system for laser interrogation of surface agents moving relative to the apparatus. A receiver telescope includes a secondary reflector that may compensate for variations in distance from a target to the laser. The secondary reflector relies on a distance to target signal output by a range finding means that may be collected at a point substantially away from the target, in the direction of relative motion, to allow a focusing mechanism time to react. The focusing means focuses the secondary reflector based on the distance-to-target signal and the rate of relative motion. An optical fiber couples inelastically scattered radiation from the secondary reflector to a spectrograph.
In a sixth aspect the invention provides a system for laser interrogation of surface agents moving relative to the apparatus. A receiver telescope includes a secondary reflector that may compensate for variations in distance from a target to the laser. The secondary reflector relies on a distance to target signal output by a range finding means that may be collected at a point substantially away from the target, in the direction of relative motion, to allow a focusing mechanism time to react. The focusing means focuses the secondary reflector based on the distance-to-target signal and the rate of relative motion. An aluminum honeycomb structure carries the components relatively rigidly with respect to one another.
The above and other features and advantages of the present invention will be further understood from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings.